Balloon catheters find widespread use in the medical field. This invention pertains to balloon catheters which are particularly used in angioplasty or PTCA, where the catheter is inserted into a blood vessel of the patient, positioned, and the balloon is expanded to widen the artery, typically in a stenotic area.
To accomplish this, it is particularly important in the field of angioplasty for the catheter to be initially as small as possible in the area of the catheter balloon, to permit insertion of the catheter through narrow apertures in the artery, such apertures being often surrounded by the stenosis. Catheters with conventional balloons have been sometime incapable of penetrating a small aperture through a stenosis, because, even though the balloon is folded and collapsed, it is slightly larger than the remainder of the catheter shaft, and thus cannot pass through the stenosis.
Also, the surgeon often must estimate the desired size of balloon inflation needed for a particular clinical situation. For this reason various angioplasty catheters with differently sized balloons are available. Often, the surgeon has to remove one catheter with one inflated size of a balloon and replace it with a catheter having a balloon of different inflated size. Typically, balloons of the prior art inflate to a given desired, predetermined size because commercial angioplasty balloons are generally made of flexible but non-resilient plastic materials. There is a significant need for balloons to have a predetermined, maximum size to avoid overinflation.
Thus, in many clinical situations a first catheter balloon that is inserted may turn out to be too small, or it may be desired for the first step of inflation to be only to a certain, smaller amount than a later inflation step. In either circumstance, another catheter balloon of larger size must be brought to bear, which either requires complex, double balloon catheters having a larger shaft, or a new catheter altogether.
In accordance with this invention, a catheter is provided which can be of very small shaft diameter, for example no more than 0.03 inch and preferably less, while at the same time carrying a catheter balloon which is initially substantially no larger than the diameter of the catheter shaft. Furthermore, by this invention, it becomes possible to inflate the same catheter balloon to two different predetermined, maximum diameters. The surgeon can reliably know the maximum diameter of the inflated balloon in predetermined circumstances from the inflation pressure applied, to avoid the danger of the balloon assuming an excessively large diameter for a particular clinical situation. Nevertheless, the same balloon may be inflated to more than one predetermined maximum diameter, so that the catheter of this invention has a greatly increased flexibility of use in surgical procedures.